The present invention relates to pharmaceutical compositions and methods of drug delivery. The invention especially relates to methods and compositions for providing controlled release of proteinaceous drugs.
Controlled drug delivery technologies have advanced significantly over the last few decades and current technologies afford delivery of drugs at predetermined rates for days and years depending on the application. These advances, however, are applicable mostly to low molecular weight drugs. It is still difficult to develop controlled release formulations for long-term delivery of high molecular weight drugs, such as peptides, proteins, oligonucleotides, and genes. The delivery of high molecular weight drugs has become especially significant since the development of recombinant DNA technology, which has made possible large-scale production of such protein drugs as tissue plasminogen activator (TPA), erythropoietin (EPO), interferon, insulin, and a number of growth factors. Furthermore, completion of the genome project is expected to result in an improved understanding of the therapeutic roles of many different proteins, which should lead to numerous new protein drugs.
Almost all protein drugs are short acting, requiring repeated injections to maintain therapeutic efficacy. Many drugs, such as human growth hormone, luteinizing hormone-releasing hormone, interferons, cyclosporins, and TPA, are therapeutically useful only by following a therapeutic regimen that may require multiple injections daily. This means that therapeutic applications and commercialization of these drugs rely heavily on the successful development of viable delivery systems, which can improve their biochemical and biophysical stability and systemic bioavailability. Development of nonparenteral routes of administration, such as oral, nasal, pulmonary, ocular, buccal, vaginal, rectal, and transdermal routes, are highly desirable, but to date delivery through such routes is very difficult, if not impossible. The high molecular weights and enzymatic degradations of protein drugs make them particularly difficult to deliver non-parenterally.
Currently, the main goal in delivery of protein-based pharmaceuticals is to develop controlled release formulations that permit long-term delivery ranging from weeks to months from a single administration. For such applications, biodegradable polymers are very attractive, especially when their degradation products are known to be innocuous or biocompatible. They need not be surgically removed at the end of a treatment. Commonly used biodegradable polymers, which have been investigated for the controlled delivery of protein drugs, include homopolymers of poly(lactic acid) (PLA) or poly(glycolic acid) (PGA), poly(lactic acid-co-glycolic acid) (PLGA), poly(ortho esters), and polyanhydrides. Of these, PLGA has been used most frequently. Due to the long history of clinical applications of PLGA, it has become a polymer of choice for developing most protein drug delivery systems. A number of excellent reviews discuss currently available microencapsulation methods (1,2).
In discussing different approaches of microencapsulation, it is useful to understand the terminologies commonly used in the microencapsulation field. The process of microencapsulation results in xe2x80x9cmicroparticles.xe2x80x9d Microparticles can be divided into xe2x80x9cmicrospheresxe2x80x9d and xe2x80x9cmicrocapsules,xe2x80x9d which are different from each other. Microspheres usually refer to a monolithic type formulation in which the drug molecules are dispersed throughout the polymeric matrix (1, 2). On the other hand, microcapsules refer to reservoir devices in which the drug core is surrounded by a continuous polymeric layer or membrane. The drug core can be single (mononuclear) or multiple (multinuclear) inside the polymer membrane (3-5), but mononuclear microcapsules are generally preferred for drug delivery.
There are a number of advantages of microcapsules over microspheres. First of all, microcapsule formulations provide much more drug reservoir space than microspheres. In microcapsules only a minimal amount of the drug compound is in contact with organic solvent during processing and with the polymer coating after the microcapsules are formed. In contrast, protein drugs in microspheres are dispersed throughout the polymer matrix, but the large contact areas between protein drugs and solid polymer component may be unfavorable for protein stability. In microcapsules, protein drugs can be further protected from degrading polymers using another layer of a hydrophilic material or matrix before microencapsulation. For example, drug-containing nanoparticles made of gelatin, agarose, or poly(vinyl alcohol) suspended in an organic solvent containing a dissolved polymer (e.g., PLGA in methylene chloride) form multinuclear microcapsules by phase separation methods (6, 7) or by solvent extraction methods (8, 9). Microcapsules also provide desirable zero-order release as compared to the ever-decreasing release rate obtained by microspheres.
The current methods used for the preparation of microencapsulated pharmaceutical products are listed below, each of which has its own advantages, limitations and drawbacks. While the methods listed have been used to produce successful commercial products, many protein drugs cannot be formulated using such methods. Considering that a large number of protein drugs are available now and will be produced in the near future, it is clear that new, improved protein delivery systems need to be developed.
Solvent evaporation and solvent extraction
Coacervation (Simple and complex coacervation)
Hot melt microencapsulation (congealing)
Interfacial cross-linking and interfacial polymerization
Spray drying
Supercritical fluid
Solvent evaporation and solvent extraction methods utilize volatile organic solvents for dissolving water-insoluble polymers, such as PLGA. Commonly used organic solvents are methylene chloride, ethyl acetate, and methyl ethyl ketone. A double emulsion process is commonly used for producing PLGA microspheres containing water-soluble drugs, including protein drugs. Both solid/oil/water (s/o/w) and water/oil/water (w/o/w) systems are used depending on the type of drug (10). A drug in soluble or dispersed form is added to the polymer solution, and the mixture is then emulsified in an aqueous phase containing a surface-active agent, such as poly(vinyl alcohol). In the solvent evaporation method, the organic solvent is evaporated by raising the temperature and/or by applying vacuum. See, for example, U.S. Pat. No. 3,523,906 (issued to Vrancken, et al.). In the solvent extraction method, the organic solvent diffuses into the water phase to make emulsion droplets into solid polymer microspheres. See, for example, U.S. Pat. No. 4,389,330 (issued to Tice, et al.). In both methods, the continuous phase can be non-miscible oils. The organic solvent conventionally employed in this method is a chlorinated hydrocarbon, such as methylene chloride, of which a residual amount is strictly controlled under 600 ppm for the known toxicities. In addition, the loading capacity of microspheres prepared by the solvent extraction and solvent evaporation is in general low. Furthermore, the way emulsions are created increases not only the total interfacial area the bioactive materials are subjected to, but also the extent of shear and cavitation stress which may be destructive to bioactive materials (12).
To minimize the loss of activity of the bioactive materials, it has been proposed to make microspheres at very low temperatures. See, e.g., U.S. Pat. No. 5,019,400 (issued to Gombotz, et al.). Biodegradable polymer is dissolved in an organic solvent, such as methylene chloride, together with protein powders, and then atomized over a bed of frozen ethanol overlaid with liquid nitrogen. The microdroplets freeze upon contacting the liquid nitrogen, and then sink onto the frozen ethanol layer. As the ethanol layer thaws, the frozen microspheres sink into the ethanol. Methylene chloride, the solvent in the microspheres, then thaws and is slowly extracted into the ethanol, resulting in hardened microspheres containing proteins and a polymer matrix. This process, which utilizes liquid nitrogen and methylene chloride, is not easy, especially for scale-up mass production.
The coacervation method is based on salting out (or phase separation) from a homogeneous polymer solution of hydrophilic polymers into (small droplets of) a polymer-rich, second liquid phase, rather than into solid aggregates. When an aqueous polymer solution (e.g., gelatin or carboxymethylcellulose) is partially dehydrated (or desolvated) by adding a strongly hydrophilic substance (e.g., sodium sulfate) or a water-miscible, non-solvent (e.g., ethanol, acetone, dioxane, isopropanol, or propanol), the water-soluble polymer is concentrated in water to form the polymer-rich phase. This is known as xe2x80x9csimplexe2x80x9d coacervation. If water-insoluble drug particles are present as a suspension or as an emulsion, the polymer-rich phase is formed on the drug particle surface to form a capsule under suitable conditions. In xe2x80x9ccomplexxe2x80x9d coacervation, the polymer-rich complex (coacervate) phase is induced by interaction between two dispersed hydrophilic polymers (colloids) of opposite electric charges. Since electrostatic interactions are involved, the pH of the medium is very important to control the charges of the polymers.
In hot melt microencapsulation (also called congealing), a solid drug or liquid drug is mixed with the polymer melted at high temperatures. The mixture is then suspended in a non-miscible solvent with continuous stirring at a temperature several degrees above the melting point of the polymer. After the emulsion is stabilized, the system is cooled until the polymer particles solidify. The drug has to be stable at the polymer melting temperature. For interfacial cross-linking, the polymer must possess functional groups that can be cross-linked by ions or multi-functional molecules. Interfacial polymerization requires monomers that can be polymerized at the interface of two immiscible substances to form a membrane, and thus removal of the unreacted monomers from the final product becomes an issue.
For spray drying, a drug is dissolved or suspended in a suitable (either aqueous or non-aqueous) solvent that contains dissolved polymer materials. The drug can be dissolved or suspended in the solvent. Alternatively, the drug solution can be emulsified in the polymer solution. The solution is atomized and microspheres are dried by a heated carrier gas. The temperature of inlet gas can be 90-150xc2x0 C. for protein drugs (14, 15). The microsphere size is controlled by the rate of spraying, the feed rate of the drug-polymer solution, the nozzle size, and temperature in the drying and cooling chambers. This seemingly simple process has not been used widely in the pharmaceutical industry due, in part, to the difficulties in the scale-up process. The parameters optimized in the laboratory scale spray drier do not usually work for the much larger industrial scale spray drier. Spray drying and hot melt microencapsulation methods have not been used as frequently as the solvent evaporation and solvent extraction methods due to the need for high temperature, which can easily denature protein drugs.
A supercritical fluid is defined as a fluid for which the temperature and pressure are simultaneously higher than those at the critical point (i.e., critical temperature Tc and critical pressure Pc), at which the density of gas is equal to that of the remaining liquid and the surface between the two phases disappears. Microparticles have been prepared by either rapid expansion of supercritical solutions (RESS) or supercritical antisolvent crystallization (SAS) (16). RESS exploits the liquid-like solvent power of the supercritical fluids whereas SAS uses supercritical fluid as an antisolvent. Carbon dioxide is most commonly used for the critical conditions are easily attainable, i.e., Tc=31xc2x0 C. and Pc=73.8 bar. It is also environmentally benign, relatively non-toxic, non-inflammable, inexpensive, and has a reasonably high dissolving power (17). RESS is limited by the constraint that all solutes should be soluble in the supercritical fluid. For this reason, RESS may not be used for protein encapsulation using polymers, because of their low solubility in common supercritical fluids. SAS is suitable for processing of solids difficult to solubilize in supercritical fluids, such as peptides and proteins. The supercritical fluid approach does not provide any significant advantages over the other methods listed above. Furthermore, the supercritical fluid approach produces only microspheres and the production of microcapsules is extremely difficult.
Protein drugs for long-term application have been most frequently formulated into microspheres made of biodegradable poly(lactic-co-glycolic acid) (PLGA). PLGA is the polymer of choice, since it has been used for a variety of clinical applications and is known to be biocompatible. For this reason, there has been little reason to use other polymers, unless use of PLGA is impossible.
Of the microencapsulation methods listed above, solvent evaporation and solvent extraction methods have been most frequently employed with PLGA, since it is not water-soluble (18). The solvent evaporation and extraction methods have had limited success with a few select therapeutic proteins (19-20). Also, see U.S. Pat. No. 5,942,253 (issued to Gombotz, et al.) and U.S. Pat. No. 6,020,004 (issued to Shah). These methods, however, are not suitable for the majority of proteins due to lengthy procedures and difficulty in scale up for mass production. In many cases, contacts between protein and solvent throughout the microsphere matrix may cause denaturation of most protein drugs to be loaded. Because of the problems associated with using organic solvents, the solvent evaporation and extraction methods have not been used as a universal method for making microparticles of protein drugs. To avoid the use of chlorinated organic solvents in microsphere formation, methylene chloride has been replaced with less toxic solvents, such as ethyl acetate, N-methylpyrrolidone, methyl ethyl ketone or acetic acid. PLGA polymer is then precipitated by adding alcohol as a non-solvent and water as a hardening agent (PCT Publication WO 01/15,799 of Benoit, et al.). In this phase separation approach, which is similar to coacervation discussed above, protein drugs have to be exposed to organic solvents for a prolonged period of time, and the prepared microspheres are prone to aggregation. In addition, the use of water as a hardening agent may not be ideal for water-soluble drugs, including protein drugs that can dissolve and leach out from the microspheres into the water phase. Since protein drugs will be directly in contact with the polymer matrix, protein molecules may adsorb to the solid surface and become denatured.
Some patent references propose use of acetic acid in the preparation of microspheres such as those made from PLGA. U.S. Pat. No. 5,100,669 (issued to Hyon et al.) propose use of glacial acetic acid to prepare a solution containing both PLGA and an active substance, such as leutenizing hormone releasing hormone (LHRH). PLGA-dissolved glacial acetic acid was mixed with 1/10 volume of aqueous solution of LHRH to obtain complete dissolution of the polymer and the active substance. This solution was added dropwise to oil to prepare an emulsion. Microspheres were obtained by removing water and acetic acid by solvent evaporation at elevated temperatures. The process was used to dissolve both PLGA and an active substance in the same solvent, e.g., acetic acid-water mixture.
U.S. Pat. No. 5,004,602 (issued to Hutchinson) and U.S. Pat. No. 5,320,840 (issued to Camble et al.) propose use of acetic acid to dissolve both PLGA and protein drugs in the same solvent. Glacial acetic acid with dissolved PLGA and protein drug were freeze dried to obtain a powder form that can be pressed at elevated temperatures. The acetic acid solution containing both PLGA and peptide drug (e.g., somatostatin analogue) was spray dried to obtain microspheres (27). In another application, PLGA was dissolved in glacial acetic acid and subsequently freeze-dried to make PLGA foams for sustained drug delivery. Clearly, acetic acid was used in the literature mainly for the purpose of dissolving PLGA and active agents in the same solvent. Protein drugs may be dispersed in the same solvents and microspheres may be made using conventional solvent extraction and evaporation methods utilizing s/o/w or w/o/w emulsions or using the spray drying method.
It is desired to develop a method of forming microencapsulated drugs, e.g., as microspheres or microcapsules, in which the drug remains substantially stable and is not denatured or inactivated by the manufacturing process. Organic solvents used in the method should not have excessive toxicities so that any incorporation into the pharmaceutical preparation does not present deleterious side effects. Especially desired are novel formulations and manufacturing methods of protein drugs, which maintain their efficacy and permit sustained and/or controlled release over extended periods.
The present invention is for an encapsulated composition and method for making the same. An encapsulated composition can be any encapsulated entity, such as those encountered in the pharmaceutical, paint, and adhesive industries. Preferably, and most generally, the encapsulated composition contains a physiologically active substance as the core material and exhibits controlled release properties. More preferably, the physiologically active substance is a protein.
A manufacturing method of the present invention comprises: (i) providing an aqueous solution composed of water and a core substance dissolved therein; (ii) providing a polymer solution composed of a water-miscible or soluble solvent and a water-insoluble polymer dissolved therein; (iii) forming a droplet of the aqueous solution containing the core substance; and (iv) admixing the droplet of aqueous solution with at least a portion of the polymer solution under conditions permitting the water-insoluble polymer to deposit on the core substance to afford the encapsulated composition. Preferably, the core substance is a protein drug and the water-insoluble polymer is biocompatible. More preferably the polymer is biodegradable, such as poly(lactic acid-co-glycolic acid) (PLGA). Particularly preferred water-miscible or soluble solvents include acetic acid, methyl acetate, ethyl acetate, and ethyl formate.
In a preferred embodiment of the invention, microdroplets of an aqueous drug (e.g., a protein) solution are contacted with microdroplets of a hydrophilic organic solvent having a polymer dissolved therein. At the interface of water and solvent, solvent exchange occurs resulting in a lowering of solvent quality for the dissolved polymer. The polymer thereby precipitates onto the surface of the aqueous microdroplets to form a membrane therearound. The desired interface between water and organic solvent can be created by many techniques, some of which were described in the examples hereinafter.
The exchange between water and organic solvent at the droplet interface is a key aspect of the present invention, thus this process is called a xe2x80x9csolvent exchange method.xe2x80x9d Only a minute fraction of protein drugs are directly exposed to the polymer solvent by this method, thereby minimizing the potential for protein denaturation. The solvent exchange method can also permit easy scale-up for mass production.
The present invention may be further understood with reference to the attached drawings, which illustrate non-limiting embodiments of the present invention.